1. Field of the Invention
The invention relates to a ferromagnetic-article sensor and, more particularly, to a ferromagnetic-article sensor using a magnetic field detection element resistive to a part of a magnetic field parallel to a magneto-resistive face.
This application is based on Japanese Patent Application No. Hei 9-049615, the contents of which are incorporated herein by reference.
2. Background Art
Japanese Patent Applications, First Publications, No. Sho 60-102585 and No. Sho 61-199875 disclose a metal ball detecting apparatus.
FIG. 7 shows the metal ball detecting apparatus of the prior art. The metal ball detecting apparatus is comprised of a holder 30 having a through-hole 40 for a metal ball 50; a permanent magnet 10 and a Hall element 60 mounted on the holder 30; and an L-shaped magnetic path 70 of ferromagnetic material connected to the permanent magnet 10 and to the Hall element 60.
The pole face of the permanent magnet 10 and the magneto-resistive face of the Hall element 60 are disposed perpendicularly to a radius of the metal ball 50 traveling through the through-hole 40.
There are restrictions on the arrangements of the permanent magnet 10, the Hall element 60, and the metal ball 50 because the metal ball detecting apparatus employs a magnetic field detection element, such as the Hall element, which is responsive to a magnetic field perpendicular to the element face. Namely, an angle between the permanent magnet face and the Hall element face must be 90 degrees, or 90.times.N degrees (N is a natural number). The magneto-resistive face of the Hall element 60 must be disposed perpendicular to a radius of the metal ball 50, in other words, parallel to a line tangential to the metal ball 50.
In addition, due to an output characteristic of the Hall element 60, which is inferior in linearity in response to a low magnetic field of less than 30 gauss, the magnetic field formed by the permanent magnet 10 must be enhanced, or a gap between the permanent magnet 10 and the Hall element 60 must be very narrow. This creates a problem in that the metal ball 50 may be attracted to the permanent magnet 10.